Light-emitting device

ABSTRACT

This disclosure discloses a light-emitting device. The light-emitting device includes a light-emitting stack having a first-type semiconductor layer, a second-type semiconductor layer, and an active layer formed between the first-type semiconductor layer and the second-type semiconductor layer; and a reflective structure formed on the first-type semiconductor layer and having a first interface and a second interface. A critical angle at the first interface for a light emitted from the light-emitting stack is larger than that at the second interface. The reflective structure electrically connects to the first-type semiconductor layer at the first interface, and an area of the first interface is more than an area of the second interface in a top view.

REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/793,611, filed on Oct. 25, 2017, which is a continuation of U.S.application Ser. No. 14/261,368, filed on Apr. 24, 2014, which claimspriority to TW application Serial No. 102114988, filed on Apr. 25, 2013,each of which is incorporated by reference herein in its entirety.

BACKGROUND Technical Field

The present disclosure relates to a light-emitting device, and inparticular to a light-emitting device comprising a reflective structure.

Description of the Related Art

The light-emitting diodes (LEDs) of the solid-state lighting elementshave the characteristics of low power consumption, low heat generation,long operational life, shockproof, small volume, quick response and goodopto-electrical property like light emission with a stable wavelength sothe LEDs have been widely used in household appliances, indicator lightof instruments, and opto-electrical products, etc. However, how toimprove a lighting efficiency of the LEDs is still an important issue.

In addition, the LEDs can be further connected to other components (suchas submount) in order to form a light emitting apparatus (ex. alight-emitting package structure). The light emitting apparatus compriseone submount with a circuit, a solder formed on the submount formounting the LEDs on the submount such that a substrate of the LEDs iselectrically connected to the circuit, and an electrical connectionstructure for electrically connecting bonding pads with the circuit. Thesubmount can be a lead frame or a mounting substrate with a larger sizefor easily designing a circuit layout thereon and for increasing heatdissipation efficiency.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a light-emitting device with areflective structure.

A light-emitting device is provided, which includes a substrate, abonding layer, a light-emitting stack, a reflective structure, a void, afirst interface and a second interface. The bonding layer is on thesubstrate. The light-emitting stack includes a first-type semiconductorlayer, a second-type semiconductor layer, and an active layer betweenthe first-type semiconductor layer and the second-type semiconductorlayer. The reflective structure is between the first-type semiconductorlayer and the substrate. The void is between the substrate and thelight-emitting stack. The first interface is between the substrate andthe light-emitting stack. The second interface is on the void. The voidis enclosed and embedded within the light-emitting device and directlyconnects to the bonding layer. The reflective structure electricallyconnects to the first-type semiconductor layer at the first interface. Acritical angle at the first interface for a light emitted from thelight-emitting stack is larger than that at the second interface.

Another light-emitting device is further provided, which includes alight-emitting stack, a reflective structure and a contact layer. Thelight-emitting stack includes a first-type semiconductor layer, asecond-type semiconductor layer, and an active layer between thefirst-type semiconductor layer and the second-type semiconductor layer.The reflective structure is on the first-type semiconductor layer andhaving a first interface and a second interface. A critical angle at thefirst interface for a light emitted from the light-emitting stack islarger than that at the second interface. The contact layer is betweenthe first-type semiconductor layer and the reflective structure. Thecontact layer includes metal or alloy. The reflective structureelectrically connects to the first-type semiconductor layer at the firstinterface. The contact layer electrically connects to the first-typesemiconductor layer.

Another light-emitting device is further provided, which includes alight-emitting stack, a reflective structure and a contact layer. Thelight-emitting stack includes a first-type semiconductor layer, asecond-type semiconductor layer, and an active layer between thefirst-type semiconductor layer and the second-type semiconductor layer.The reflective structure is on the first-type semiconductor layer andhaving a first interface and a second interface. A critical angle at thefirst interface for a light emitted from the light-emitting stack islarger than that at the second interface. An area of the first interfaceis larger than an area of the second interface in a top view. Thecontact layer is between the first-type semiconductor layer and thereflective structure. The reflective structure electrically connects tothe first-type semiconductor layer at the first interface. The contactlayer electrically connects to the first-type semiconductor layer.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawings are included to provide easy understanding ofthe application, and are incorporated herein and constitutes a part ofthis specification. The drawings illustrate the embodiments of theapplication and, together with the description, serves to illustrate theprinciples of the application.

FIG. 1 shows a cross-sectional view of a light-emitting device inaccordance with one embodiment of the present disclosure.

FIG. 2 shows a top view of the light-emitting device in accordance withone embodiment of the present disclosure.

FIGS. 3A-3E are cross-sectional views illustrating a method of making alight-emitting device in accordance with one embodiment of the presentdisclosure.

FIGS. 4A-4H are cross-sectional views illustrating a method of making alight-emitting device in accordance with another embodiment of thepresent disclosure.

FIGS. 5A and 5B illustrate a top view of a patterned sacrificial layerand a transparent conductive layer.

FIG. 6 illustrates a cross-sectional of a light-emitting device inaccordance with another embodiment of the present disclosure.

FIG. 7 illustrates an explorer view of a bulb using the light-emittingdevice.

DETAILED DESCRIPTION OF THE EMBODIMENTS

To better and concisely explain the disclosure, the same name or thesame reference number given or appeared in different paragraphs orfigures along the specification should has the same or equivalentmeanings while it is once defined anywhere of the disclosure.

The following shows the description of embodiments of the presentdisclosure in accordance with the drawings.

FIG. 1 is a cross-sectional view of a light emitting device 100 inaccordance with one embodiment of the present disclosure. As shown inFIG. 1, the light-emitting device comprises a substrate 10, a bondingstructure 12 formed on the substrate 10, a reflective structure 14formed on the bonding structure 12, a light-emitting stack 16 formed onthe reflective structure 14, a first electrode 19 formed on thesubstrate 10 and a second electrode 18 formed on the light-emittingstack 16. The bonding structure 12 comprises a first bonding layer 121,a second bonding layer 12 and a third bonding layer 123. The reflectivestructure 14 comprises a metal layer 141 formed on the first bondinglayer 121, a transparent conductive layer 142 formed on the metal layer141, and a void 143 formed between the transparent conductive layer 142and the light-emitting stack 16. The light-emitting stack 16 comprises afirst-type semiconductor layer 161, an active layer 162 formed on thefirst-type semiconductor layer 161 and emitting a light, and asecond-type semiconductor layer 163 formed on the active layer 162. Thefirst-type semiconductor layer 161 and the second-type semiconductorlayer 163, for example a cladding layer or a confinement layer,respectively provide electrons and holes such that electrons and holescan be combined in the light-emitting layer 162 to emit light. In thisembodiment, the first-type semiconductor layer 161 directly contacts thetransparent conductive layer 142 to form a first interface 144therebetween, and the first-type semiconductor layer 161 directlycontacts the void 143 to form a second interface 145 therebetween. Thevoid 143 is formed within the transparent conductive layer 142 and doesnot directly contact the metal layer 141. Furthermore, the void 143 hasa refractive index smaller than that of the transparent conductive layer142. In other words, a difference of the refractive index between thefirst-type semiconductor layer 161 and the transparent conductive layer142 is smaller than that between the first-type semiconductor layer 161and the void 143. Therefore, when the light emitted by the active layer162 progresses toward the reflective structure 14, a critical angle ofthe light at the first interface 144 is larger than that at the secondinterface 145, that is, the probability occurring the total internalreflection at the second interface 145 is larger than at the firstinterface 144. In addition, the first-type semiconductor layer 161ohmically contacts the transparent conductive layer 142 at the firstinterface 144 and the first-type semiconductor layer 161 non-ohmicallycontacts the void 143 at the second interface 145.

FIG. 2 is a top view of the light-emitting device 100 in accordance tothe embodiment of the present disclosure. FIG. 1 is a cross-sectionalview taken along line AA′ of FIG. 2. In this embodiment, the secondelectrode 18 has an electrode pad 180 and a plurality of first extensionelectrodes 181, a plurality of second extension electrodes 182 and aplurality of third extension electrodes 183. The plurality of firstextension electrodes 181 extends from the electrode pad 180 along the Xdirection toward opposite sides (right and left) of the light-emittingdevice 100 and arranged in a line. The plurality of second extensionelectrodes 182 extends from the electrode pad 180 along the Y directiontoward opposite sides (up and down) of the light-emitting device 100 andarranged in a line. The second extension electrodes 182 areperpendicular to the first extension electrodes 181. The plurality ofthird extension electrodes 183 is physically connected to the secondextension electrodes 182 and electrically connected to the electrode pad180. The third extension electrodes 183 are arranged in parallel withthe first extension electrodes 181. The first extension electrodes 181are disposed between the third extension electrodes 183. A distancebetween the first extension electrodes 183 and the third extensionelectrodes 181 can be the same or different. The void 143 are formedbelow portions of the first extension electrodes 181 and the thirdextension electrodes 183 and has a width larger than the correspondingfirst extension electrode 181 and the third extension electrode 183 inthe Y direction. The void 143 is not formed below the electrode pad 180and portions of the second extension electrodes 182. The void 143 ismerely formed at a position corresponding to the extension electrodes181, 183 and extends to two opposite sides of the light-emitting device100. In this embodiment, the void 143 is not formed below the firstextension electrode 181 close to the electrode pad 180. The void 143corresponding to the third extension electrode 183 has a length largerthan that of the third extension electrode 183 in the X direction. Inanother embodiment, the quantity and the arrangement of the electrodeextensions can be varied depending on actual requirement.

In this embodiment, the first-type semiconductor layer 161 is a p-typesemiconductor layer and the second-type semiconductor layer 163 is ann-type semiconductor layer. Alternatively, the first-type semiconductorlayer 161 is an n-type semiconductor layer and the second-typesemiconductor layer 163 is a p-type semiconductor layer. The first-typesemiconductor layer 161 and the second-type semiconductor layer 162comprise one of AlGaAs, AlGaInP, AIlnP, InGaP, GaP, and GaAs, or one ofAlInGaN, InGaN, AlGaN and GaN. The dopant in the p-type semiconductorlayer comprises Mg, Be, Zn, C or combinations thereof. The dopant in then-type semiconductor layer comprises Si, P, As, Sb or combinationsthereof. The active layer 162 comprises one of AlGaAs, AlGaInP, AIlnP,InGaP, GaP, and GaAs, or one of AlInGaN, InGaN, AlGaN and GaN. Theactive layer can have a structure including single heterostructure (SH),double heterostructure (DH), or double-side double heterostructure(DDH), or multi-quantum well (MQW) structure. The substrate comprisesGaAs, GaP, Ge, sapphire, glass, diamond, SiC, Si, GaN, ZnO, or othersuitable material. The metal layer can be a single layer or amulti-layer and comprises Ag, Al, Au, Ni or combinations thereof. Thefirst bonding layer, the second bonding layer, and the third bondinglayer can be a single layer or a multi-layer, and comprise a metalmaterial or a glue material. The metal material comprises Au, In, Sn,Ti, Pt, or combination thereof. The glue material comprises BCB, epoxy,or PDMS, silicone (SiO_(x)), Al₂O₃, TiO₂, SiN_(x) or combinationsthereof. The transparent conductive layer can comprise metal oxide, suchas ITO, InO, SnO, CTO, ATO, AZO, ZTO, GZO, ZnO, IZO, IGO, GAZO, ordiamond-like carbon or GaP. The void can contain air, N₂, He, or Ar.

FIGS. 3A-3E are cross-sectional view showing a method of making thelight-emitting device 100 in accordance with the embodiment of thepresent disclosure. As shown in FIG. 3A, a growth substrate 20 (forexample, GaAs) is provided and a light-emitting stack 16 is epitaxiallygrown on the growth substrate 20. The light-emitting stack 16sequentially includes the second-type semiconductor layer 163 (forexample, AlGaInP), the active layer 162 (for example, AlGaInP) and thefirst-type semiconductor layer 161 (for example, GaP). As shown in FIG.3B, a sacrificial layer 15 (for example, SiO₂) is formed on thefirst-type semiconductor layer 161. In another embodiment, thesacrificial layer 15 can comprise photoresistor, SiN_(x), or metal (suchas Ni). As shown in FIG. 3C, a lithography process is conducted topattern the sacrificial layer 15 for forming a patterned sacrificiallayer 151. A transparent conductive layer 142 (for example, ITO) isformed on the patterned sacrificial layer 151 and the first-typesemiconductor layer 161 to enclose the patterned sacrificial layer 151therein. As shown in FIG. 3D, a metal layer 141 (for example, Ag) isformed on the transparent conductive layer 142. The first bonding layer121 and the second bonding layer 122 are formed on the metal layer 141.The third bonding layer is formed on a substrate (for example, Si). Bybonding the second bonding layer 122 and the third bonding layer 123together, the substrate 10 is boned to the metal layer 141. In anotherembodiment, the first bonding layer 121 comprises a multi-layer (forexample, Ti/Pt/Au). Ti layer can be used as a barrier layer to preventthe metal of the metal layer 141 from diffusing into the bonding layer;Pt layer can be used as an adhesion layer to improve adhesion between Tilayer and Au layer. As shown in 3E, the patterned sacrificial layer 151is removed using an etching method to form the void 143. The etchingmethod comprises a vapor etching method or a liquid etching method. Thevapor etching method can use vapor HF as an etchant, and the liquidetching method can use NaOH, HF, NH₄F or a mixture thereof as anetchant. After removing the growth substrate 20 to expose thesecond-type semiconductor layer 163, the first electrode 19 is formed onthe substrate 10 and the second electrode 18 is formed on thesecond-type semiconductor layer 163. The second electrode 18 comprisesthe electrode pad 180 and the extension electrodes 183. The extensionelectrodes 183 are at positions corresponding to the voids 143. Inanother embodiment, the growth substrate can be removed and then theetching is conducted to remove the patterned sacrificial layer 151. Itis noted that when the patterned sacrificial layer 151 is etched usingthe vapor etching method, since the vapor etching method does notincludes liquid (such as water), the first-type semiconductor layer 161and the transparent conductive layer 142 are not adhered to each otherdue to a surface force after removing the patterned sacrificial layer151. Therefore, the patterned sacrificial layer 151 and the voids 143have substantially the same shape. In addition, the patternedsacrificial layer 151 can have a height smaller than 800 Å, that is, thevoid 143 also has a height smaller than 800 Å.

FIGS. 4A-4H are cross-sectional view showing a method of making thelight-emitting device 200 in accordance with another embodiment of thepresent disclosure. The light-emitting device 200 has a structuresimilar with the light-emitting device 100. The devices, elements orsteps with similar or the same symbols represent those with the same orsimilar functions. As shown in FIG. 4A, a growth substrate 20 (forexample, GaAs) is provided and a light-emitting stack 16 is epitaxiallygrown on the growth substrate 20. The light-emitting stack 16sequentially includes the second-type semiconductor layer 163 (forexample, AlGaInP), the active layer 162 (for example, AlGaInP) and thefirst-type semiconductor layer 161 (for example, GaP). As shown in FIG.4B, a sacrificial layer 15 (for example, SiO₂) is formed on thefirst-type semiconductor layer 161. As shown in FIG. 4C, a lithographyprocess is conducted to pattern the sacrificial layer 15 for forming apatterned sacrificial layer 151′. A transparent conductive layer 142(for example, ITO) is formed on a portion of the patterned sacrificiallayer 151′ and the first-type semiconductor layer 161, and thetransparent conductive layer 142 does not fully enclose the patternedsacrificial layer 151 so another portion of the patterned sacrificiallayer 151′ is exposed. As shown in FIG. 4D, a metal layer 141 is formedon the transparent conductive layer 142. A protection layer 17 is formedto cover the transparent conductive layer 142 and a sidewall of themetal layer 141 and a portion of the exposed patterned sacrificial layer151′. As shown in 4E, the patterned sacrificial layer 151′ is removedusing a vapor etching method (such as, vapor HF as etchant) to form thevoid 143. Subsequently, as shown in FIG. 4F, after removing theprotective layer 17, the first bonding layer 121 is formed to cover orenclose a sidewall of the transparent conductive layer 142 and asidewall of the metal layer 141, thereby the void 143 can be embeddedwithin the first bonding layer 121 or between the first bonding layer121 and the transparent conductive layer 142. The first bonding layer121 can be a single layer or a multi-layer. In one embodiment, the firstbonding layer 121 is a multi-layer (for example, Ti/Pt/Au). Ti layer canbe used as a barrier layer to prevent the metal of the metal layer 141from diffusing into the bonding layer; Pt layer can be used as anadhesion layer to improve adhesion between Ti layer and Au layer. Asshown in 4G, by bonding the first bonding layer 121, the second layer122, and the third bonding layer 123 together, the substrate 10 (forexample, Si) is boned to the light-emitting stack 16. As shown in FIG.4H, after removing the growth substrate 20, the first electrode 19 isformed on the substrate 10 and the second electrode 18 formed on thesecond-type semiconductor layer 163. In this embodiment, the secondelectrode 18 is not formed at a position corresponding to the voids 143.The first-type semiconductor layer 161 directly contacts the transparentconductive layer 142 to form the first interface 144, the first-typesemiconductor layer 161 directly contacts the void 143 to form thesecond interface 145, and the first-type semiconductor layer 161directly contacts the first bonding layer 121 to form a third interface146. The void 143 does not directly contact the metal layer 141.Furthermore, the void 143 has a refractive index smaller than that ofthe transparent conductive layer 142 and that of the first bonding layer121. In other word, a difference of the refractive index between thefirst-type semiconductor layer 161 and the transparent conductive layer142 is smaller than that between the first-type semiconductor layer 161and the void 143. A difference of the refractive index between thefirst-type semiconductor layer 161 and the first bonding layer 121 issmaller than that between the first-type semiconductor layer 161 and thevoid 143. Therefore, when the light emitted by the active layer 162progresses toward the reflective structure 14, critical angles of thelight at the first interface 144 and at the third interface 146 arelarger than that at the second interface 145, that is, the probabilityoccurring the total reflection at the second interface 145 is largerthan at the first interface 144 and at the third interface 146. It isnoted that when the active layer 162 emits a blue light with a peakwavelength of 430 nm-480 nm, the first bonding layer 121 has arefractive index for the blue light smaller than that that of thetransparent conductive layer 142. For example, when the first bondinglayer 121 is Ti or Pt, and the transparent conductive layer 142 is ITO,the first bonding layer 121 has the refractive index of 1.6-1.9 and thetransparent conductive layer 142 has the refractive index of 2.0-2.3which indicates the critical angle of the blue light at the firstinterface 144 is larger than that at the third interface 146. Therefore,the probability occurring the total reflection at the third interface146 is larger than at the first interface 144. When the active layer 162emits a red light with a peak wavelength of 630 nm-670 nm, the firstbonding layer 121 has a refractive index for the red light larger thanthat that of the transparent conductive layer 142. For example, when thefirst bonding layer 121 is Ti or Pt, and the transparent conductivelayer 142 is ITO, the first bonding layer 121 has the refractive indexof 2.0-2.3 and the transparent conductive layer 142 has the refractiveindex of 1.7-1.9 which indicates the critical angle of the red light atthe third interface 146 is larger than that at the first interface 144.Therefore, the probability occurring the total reflection for the redlight at the first interface 144 is larger than at the third interface146. Whatever the active layer 162 emits, the void 143 has a refractiveindex of about 1. In addition, the first-type semiconductor layer 161ohmically contacts the transparent conductive layer 142 at the firstinterface 144; the first-type semiconductor layer 161 non-ohmicallycontacts the void 143 at the second interface 144; and the first-typesemiconductor layer 161 non-ohmically contacts the first bonding layer121 at the third interface 146.

FIGS. 5A and 5B illustrate top views of the patterned sacrificial layer151″ and the transparent conductive layer 142 of a light-emitting devicein accordance with an embodiment of the present disclosure. As shown inFIG. 5A, the patterned sacrificial layer 151″ comprises a plurality ofelongated structures and the transparent conductive layer 142 is formedon the elongated structures and covers portions of the elongatedstructures. As shown in FIG. 5B, the patterned sacrificial layer 151′″comprises a plurality of elongated structures perpendicular to eachother to form a net structure. The transparent conductive layer 142 isformed on the net structure and covers portions of the net structure. Inone embodiment, a surface area ratio of the patterned sacrificial layer151″, 151′″ to the first-type semiconductor layer 161 ranges from 10% to90%, or from 50% to 90%. However, the surface area, shape and quantityof the patterned sacrificial layer 151″, 151′″ can be varied dependingon actual requirements. A surface area ratio of the transparentconductive layer 142 to the first-type semiconductor layer 161 rangesfrom 10% to 90%, or from 10% to 50%. It is noted that, based on theaforesaid description, since the void is formed by removing thesacrificial layer, the void has a substantially shape or structure sameas that of the sacrificial layer. Therefore, the void has an elongatedstructure or a net structure.

FIG. 6 illustrates a cross-sectional view of a light emitting device 300in accordance with an embodiment of the present disclosure. Thelight-emitting device 300 has a structure similar with thelight-emitting device 200. The devices, elements or steps with similaror the same symbols represent those with the same or similar functions.In this embodiment, the light-emitting device 300 further comprises acontact layer 147 formed between the first-type semiconductor layer 161and the transparent conductive layer 142 for spreading current. Thecontact layer 147 is enclosed or embedded within the transparentconductive layer 142, but does not directly contact the metal layer 141.In addition, the void 143 is formed between the contact layer 147 andthe first bonding layer 121 and to surround the contact layer 147. Thefirst-type semiconductor layer 161 directly contacts the contact layer147 to form a fourth interface 148 and to form an ohmic contacttherebetween. The contact layer 147 comprises metal or alloy. The metalcomprises Cu, Al, In, Sn, Au, Pt, Zn, Ag, Ti, Ni, Pd, Pb or Cr; and thealloy can be Be—Au, Ge—Au, Cr—Au, Ag—Ti, Cu—Sn, Cu—Zn, Cu—Cd, Sn—Pb—Sn,Sn—Pb—Zn, Ni—Sn, or Ni—Co.

FIG. 7 is an explorer view of a bulb 30 using the previously describedlight-emitting device. The bulb 30 comprises a cover 21, a lens 22, alight-emitting module 24, a holder 25, a heat sink 26, a connector 27,and a circuit element 28. The light-emitting module 24 includes acarrier 23 and a plurality of light-emitting unit. The light-emittingdevice previously described (such as the light-emitting device 100, 200or 300) can be used as the light-emitting unit. As shown in FIG. 7,twelve light-emitting units are disposed on the carrier 23 wherein thereare six red light-emitting units emitting red light and six bluelight-emitting units emitting blue light. The twelve light-emittingunits are alternately arranged and electrically connected to each other(in a series connection, in a parallel connection or a bridgeconnection). The blue light-emitting units comprise a wavelengthconversion material formed thereon for converting the blue light. Theblue light and the converted light are mixed to become a white light,and further to combine with the red light-emitting units to make thebulb 30 emit a warm white light having a color temperature of2400K-3000K.

The foregoing description has been directed to the specific embodimentsof this invention. It will be apparent to those having ordinary skill inthe art that other alternatives and modifications can be made to thedevices in accordance with the present disclosure without departing fromthe scope or spirit of the disclosure. In view of the foregoing, it isintended that the present disclosure covers modifications and variationsof this disclosure provided they fall within the scope of the followingclaims and their equivalents.

What is claimed is:
 1. A light-emitting device, comprising: a substrate;a bonding layer on the substrate; a light-emitting stack on the bondinglayer and having a first-type semiconductor layer, a second-typesemiconductor layer, and an active layer between the first-typesemiconductor layer and the second-type semiconductor layer; areflective structure between the first-type semiconductor layer and thesubstrate; a void between the substrate and the light-emitting stack; afirst interface between the substrate and the light-emitting stack; anda second interface on the void; wherein the void is enclosed andembedded within the light-emitting device and directly contacts thebonding layer, the reflective structure electrically connects to thefirst-type semiconductor layer at the first interface, and a criticalangle at the first interface for a light emitted from the light-emittingstack is larger than that at the second interface.
 2. The light-emittingdevice of claim 1, wherein the reflective structure comprises atransparent conductive layer, and the first interface is between thefirst-type semiconductor layer and the transparent conductive layer. 3.The light-emitting device of claim 1, further comprising an electrode onthe light-emitting stack, wherein the electrode comprises an electrodepad, a first extension electrode connecting to the electrode pad.
 4. Thelight-emitting device of claim 3, wherein the void is at a position notvertically aligned to the electrode pad.
 5. The light-emitting device ofclaim 3, wherein the electrode further comprises a third extensionelectrode extending from the electrode pad and having a portion at aposition vertically aligned to the void.
 6. The light-emitting device ofclaim 1, further comprising an electrode on the light-emitting stack,wherein the electrode comprises an electrode pad, and from a crosssection view of the light-emitting device, the first interface at aposition vertically aligned to the electrode pad has a first widthlarger than a second width of the electrode pad.
 7. The light-emittingdevice of claim 1, wherein the reflective structure electricallyconnects to the first-type semiconductor layer at the first interface.8. The light-emitting device of claim 1, wherein the second interface isbetween the first-type semiconductor layer and the void.
 9. Thelight-emitting device of claim 1, wherein the second interface is at aposition vertically aligned to the void.
 10. The light-emitting deviceof claim 1, further comprising an electrode on the light-emitting stack,wherein the electrode comprises an electrode pad and a first extensionelectrode connecting to the electrode pad, and the second interface isat a position vertically aligned to a portion of the first extensionelectrode and at a position not vertically aligned to the electrode pad.11. A light-emitting device, comprising: a light-emitting stackincluding a first-type semiconductor layer, a second-type semiconductorlayer, and an active layer between the first-type semiconductor layerand the second-type semiconductor layer; a reflective structure having afirst interface and a second interface, wherein a critical angle at thefirst interface for a light emitted from the light-emitting stack islarger than that at the second interface; a contact layer between thefirst-type semiconductor layer and the reflective structure, wherein thecontact layer includes metal or alloy and electrically connects to thefirst-type semiconductor layer; and an electrode pad on the second-typesemiconductor layer; wherein the reflective structure electricallyconnects to the first-type semiconductor layer at the first interface,and the first interface has a portion at a position vertically alignedto the electrode pad.
 12. The light-emitting device of claim 11, whereinthe reflective structure includes a transparent conducive layer.
 13. Thelight-emitting device of claim 11, wherein the contact layer directlycontacts the first-type semiconductor layer to form an ohmic contact.14. The light-emitting device of claim 11, wherein the reflectivestructure includes a metal layer and the contact layer does not contactthe metal layer.
 15. The light-emitting device of claim 11, furthercomprising an extension electrode extending from the electrode pad,wherein the second interface has a portion at a position verticallyaligned to the extension electrode.
 16. A light-emitting device,comprising: a light-emitting stack including a first-type semiconductorlayer, a second-type semiconductor layer, and an active layer betweenthe first-type semiconductor layer and the second-type semiconductorlayer; a reflective structure having a first interface and a secondinterface, wherein a critical angle at the first interface for a lightemitted from the light-emitting stack is larger than that at the secondinterface, and an area of the first interface is larger than an area ofthe second interface in a top view; a contact layer between thefirst-type semiconductor layer and the reflective structure, andelectrically connects to the first-type semiconductor layer; and anelectrode pad on the second-type semiconductor layer; wherein thereflective structure electrically connects to the first-typesemiconductor layer at the first interface, and the first interface hasa portion at a position vertically aligned to the electrode pad.
 17. Thelight-emitting device of claim 16, wherein the reflective structureincludes a transparent conducive layer.
 18. The light-emitting device ofclaim 16, further comprising a bonding layer connected to the reflectivestructure and directly contacts the first-type semiconductor layer. 19.The light-emitting device of claim 16, wherein the reflective structureincludes a metal layer and the contact layer does not contact the metallayer.
 20. The light-emitting device of claim 16, further comprising anextension electrode extending from the electrode pad, wherein the secondinterface has a portion at a position vertically aligned to theextension electrode.